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Home>Props Comparison

New Prop Test Comparisons

 

 

From top to bottom

66" Bolly
70" Bolly
69" Kool
69" Aon
71" Kiev
(The spots on the blades are for measuring pitch at 600mm from centres)

 

For these tests, the props were pitched to give 5200 rpm at best climb rate of 57 kts.
Rotax specifies that rpm at climb should not be less than 5200.
This pitch gives 5900 at wide open throttle (WOT) straight and level with two props. 
This is 100 rpm above the red line, but to pitch for 5800 WOT will give a climb at less than 5200.
We never run WOT straight and level anyhow, but we do climb every time we fly, so I'll set for 5200.

 

The test flights using manifold pressure as the reference, gave incredibly equal results for all props – all within one knot of each other!   One knot is less than the tolerance of the measuring ability.
So effectively, each prop gave exactly the same speed for the same power setting!

Engine power is RPM x Torque, so any testing that only compares at RPM settings isn't testing at the same power output.  ie- If the prop is pitched for 5500 WOT rather than 5800, then cruising at 5000 will show a higher speed, but of course that's at a much higher percentage of total power than if WOT was 5800.  Ideally we should test at equal fuel flow rates, because that truely indicates engine power, but that's difficult to determine accurately in real time.  I've tried fuel flow meters, and don't find them accurate enough, at these flow rates, to be useful for good test comparison.  The only way I've found to get truely accurate fuel flow measurement is to measure the fuel used on a three hour flight at a constant power setting, which gets a bit time consuming for multiple tests. 

 

As I understand it, manifold pressure is quite a good indicator of actual engine power output, provided altitude and air density are equal.   So I've done the cruise speed comparisons at equal manifold pressures, all at 2000' QNH, and all at very similar atmospheric conditions.

 

 

Flight Test Results

 

 

Kool  69"

Kiev  71"

Bolly  70"

Bolly  66"

AonProp  69"

WOT (rpm) 

5900 

5900 

5810 

5800 

5800 

Pitch
@ 600mm 

16.5 

16.25 

19 

20 

1

Time to Climb
2000-3000 ft
(sec)

60 

60 

60 

76 

60 

RPM
@ 57 kts climb
 

5170 

5170 

5200 

5240 

5230 

Static Thrust (kg) 

164 

162 

163 

??? 

173 

Static RPM 

4930 

5070 

5230 

??? 

5240 

MAP @ 2000ft 

kts / rpm

kts / rpm

kts / rpm

kts / rpm

kts / rpm

26"

92 @5610

92 @5490

93 @5500

92 @5500

93 @5500

25" 

85 @5160

86 @5160

85 @5030

85 @5230

86 @5200

24" 

79 @4910 

80 @4840 

79 @4800

79 @4850

79 @4800

23" 

74 @4660

75 @4640

??? 

75 @4630

75 @4500

 

 

 

 

 

 

 

It's interesting to have a look at the differences in profile and helix between different props,

but the performance is very much equal.

     

          AonProp                              Kiev                                 Kool 

 

Analysis

Just as in the earlier prop tests, I could find no real difference in cruise speed between any of the props tested, when equal power was carefully applied to each.

So it would seem that when someone claims a big difference with a different prop, they are probably depending solely upon RPM, and are actually applying more less power.

The only difference found was that the smaller diameter Bolly was considerably degraded in climb.
This has been confirmed by two real life cases that I know of, who changed from the 66" Bolly to the 70", and both reported considerably better take-off and climb performance.

 

Kool

 
                              Kool                                          Kool hub                                      Kool tip
 
  
The Kool prop is made in the Ukraine, and is beautifully designed.  It’s like a piece of sculpture, with flowing lines and not a flat spot anywhere.  Even the back surface is slightly concave.  The airfoil is thick and highly cambered, like a high-lift wing, and has a wide chord.  The core must be foam to have this light weight, but the thickness of the section, with the carbon fibre skin, makes a blade with great rigidity and stiffness.  The surface is a mirror-finish gloss black gel coat that looks great when new, but it does mark easily.....  The leading edge protection is stainless steel, moulded into the leading edge at manufacture, with ‘rivets’ embedded in the composite going right through from one side of the blade to the other.

It runs as smooth, and stops with much less jolt than the Warp.  Ground observers noted that the noise produced at cruise and full power at 800ft AGL was considerably less than the Warp.  Kool also produces a version with anti-vortex tips to reduce noise even further.  I know of a Savannah that has that prop, and we’ll do a noise comparison when we can get together.

The hub is fairly plain, with a matt black finish.  It uses the standard 75mm bolt pattern.

For 5200rpm in climb, the pitch at 600mm from the centre measured 16.5º. 

I've decided that this is my favorite prop. 

Very strong and smooth running.  Very good L/E protection.
I have about 400 hrs on it now, mostly on grass and dirt strips, and it's still looking good.

Also the best price by far, at least in Australia.  Other locally made and imports are from $1400-1800.

The Kool is US$890 plus $120 shipping direct from Canada. 
I don't feel the need of a local importer/dealer in these days of on-line shopping.  In case of problems, a local middle-man is just another obstacle to go through - I'd rather deal direct with the main man.  Vasili at http://www.airtrikes.net/propellers.shtml in Canada seems to be the main disributer for much of the world, and I've found him good to deal with.  That propellor page of his website doesn't seem to have a price list, but you can find Kool Props way down the page at http://www.airtrikes.net/airtrikes_pricelist.htm

 

Bolly
  
       Bolly                                                                  Bolly hub
  
  

The Bolly props are an Australian design and well-known here as a high quality prop.  They tried having them made in China, but weren't satisfied with the quality, so are now manufacturing in Australia again.  They're now under new ownership with big plans to become a world prop manufacturer. 

Hans started with a Woodcomp on his 701, but it snapped off cleanly at the junction to the hub when it nicked the ground while taxiing through a dip.....  (The butt of the blade was seen to be hollow!).  He used his first Bolly  for about 600hrs and loved it, until dropping the nose wheel into a rabbit hole destroyed it.....  He immediately replaced it with a new Bolly.

 The Bolly blades are considerably lighter than the Warp Drive blades, so the rotational inertia is noticeably less.  This makes it smoother running, and considerably less jolt on start and stop.  The blades are wider than the Warp and a more rounded shape as seen in the photos.  The 'Duratuf' leading edge protection is a heat-cured polyurethane, moulded into the leading edge.  It’s resilient and very effective protection against chipping.  The Bolly hub also uses the 101.6mm bolt pattern and drive lug system, particularly suitable for the 100hp engine.  It's very nicely machined, solid, and attractive so it doesn't really need a spinner.

The labelling of this BOS range of Bolly props is a bit strange.....
The so-called 72" prop is really 70", and the so-called 68" is really 66"???
So I've used the actual diameter when refering to them in the test results.
 

The tips of the Bolly aren’t flat, so can’t measure pitch at the tip.  So I used the standard 600mm (2ft) out from the centre, where it measured 19º for 5800rpm WOT..

 

Kiev

I don't have photos of the Kiev, but it's a slim, elegant prop.
Very efficient, and smooth running.  Considered to be a standard as among the most efficient.

A friend has one for 400 hrs on these dirt strips, and it's showing it's wear more than the the Bolly or Kool.
The brass leading edge is considerably dented and tarnished, but still performing well.

There can be a delay in getting one, as they can't seem to keep up to demand.

 

AonProp

light.avia@gmail.com
The AonProp company sent me this one for testing.  It's made in the Ukraine, to much the same good standard as the Kiev and Kool.
One problem that I found is that the large helix in close to the base meant that I required a 20mm spacer to fit it on my Savannah so that it cleared the cowling.....
It gave the best static thrust, but as a wise guy once said, "....That's irrelevant because you don't fly tied up to a tree anyhow...."  Well, quite right, static thrust doesn't really mean much even in take-off performance.  I've found that it only affects the very initial part of the take-off roll, and as soon as the aircraft is rolling a few miles an hour any advantage in static thrust is nullified.....

 

 

.......................................................................................................................................................................

Earlier Prop Comparisons

This is from an earlier prop test comparison.
Manifold pressure readings aren't quite comparable due to a different gauge used,
but the results are the same, in that all props gave the same speed for the sme power.
Even props as completely different as the Peszke and the Brolga!

 
 
Peszke
Bollie
Warp Drive
 
 
Warp Drive
Kool
 
 
Testing Procedure
 
I’ve long wanted to find some head-to-head comparisons of different propellers. There are many accounts of someone trying a new prop and reporting amazing results but I never found any tests that had been well-controlled to get the base line equal. 
 
The prop I had been using for 400hrs was performing well enough, but I wanted to see if I could do better. Then I had the opportunity to borrow and try several quite different brands of props.  I enjoy experimenting, and testing for real results, so took on the project.  It’s not as easy at it would seem to get fair comparisons – first, lots of short flights and pitch adjusting to get WOT (Wide Open Throttle) straight and level rpm exactly equal for each.  (I sure don’t like thundering along at full throttle, with the ASI off-scale, 100+kts, just under Vne for this Savannah aircraft....)  Then lots and lots of short flights to swap props and compare under equal conditions.  I got really quick at bolting and unbolting props......
 
My aircraft is a Savannah, originally with leading edge slats but now with the slats removed, and VGs on the original airfoil.  The engine is a Rotax 912ULS, 100hp.  All test flights were at 2000’ QNH, about 1600’ AGL here.  I installed a digital tacho to get repeatable rpm.  Had a manifold pressure gauge calibrated by an instrument shop.  Flew 4-way GPS legs with a VSI for level flight (the only way to get true speed comparisons).  Kept the fuel weight very near equal.  Temperature and atmospheric conditions very near equal (approx 23ºC).  Did the comparison runs at first light for most stable air.  Swapping the props took only minutes so the conditions were very much equal.  Did the whole procedure over and over again to eliminate anomalies and averaged the results.  Then found that the results were so much the same for each that I didn’t believe them, so did it all over again.  But they came out the same yet again.......  After a fuel bill of $500 in one month, I was satisfied with the results as being true and fair. 
 
Some will immediately say they get higher climb rates and better speed than this, and often I seem to get those indications as well in general flying, but repeatable results under same conditions is what I’m after here.
 

Pitch was measured with a Warp Drive protractor – a very good instrument, worth getting whatever prop you are  using.  It’s very easy to use and gets repeatable results right down to a quarter of a degree.

                Warp Drive protractor                                                     Thrust testing

 

 
Results
 
The results obtained are very interesting and quite surprising.  And somewhat disappointing as well - I had hoped to find some dramatic differences that would get me a prop that’s far superior to others.  Not so, the results show that there is very little difference at all between quite different props.  When I first got those results that are so much the same, I thought it must have been a coincidence, so had to do it all over again, and then again.  It just seemed unlikely that that they could come out so much the same!
 
A couple of times when I first tried a new prop I got excited by a considerably higher indicated air speed, but each time when the pitch was adjusted to the same WOT reference of 5800rpm, the 4-way GPS speed at 5000rpm came out pretty much equal to the others.
 
The test flights using manifold pressure as the reference gave even more equal results – all within one knot of each other!  As I understand it, manifold pressure is a very good indicator of actual engine power output.  Effectively each prop gave exactly the same speed for the same power setting!  That’s one test that I just had to do once again last weekend, and the result was the same yet again.....
 
The only real differences showed up in the static thrust tests.  The biggest difference was between the Peszke and the Kool, and still only 12kg out of 190kg, about 6%.  But yet, time-to-climb to 1000ft AGL for all of them was very much the same.  Time-to-climb from take-off is difficult to compare precisely because it’s so much effected by variations in getting stabilized at climb speed, more chance of variations in lift or sink in the surrounding air, and of course air temperature (even at first light there are often layers of different temperature air at these levels).  But after many climbs, all the props showed the same range of times, and averaged about 60 seconds. 
 
Of course many other users out there will claim they get different performance with their props - some of them almost magical......  But this is what I found, after really careful testing.  I have no reason to promote or demote any one prop against another.  It's been a lot of effort for no dramatic results, but at least it measures some realities.......
 
 

 

Warp Drive

Bollie

Peszke

Kool

Brolga

 

70"

70"

68"

70"

68" 4-blade

 

 

 

 

 

 

WOT (rpm)

5800

5800

5800

5800

6000

Pitch at tip (degrees)

12.5*

***

??

11.25*

16* at hub

Pitch at 600mm from centre

19.5*

19*

 

17.5*

 

 

 

 

 

 

 

@ 5000rpm (knots)

81

82

81

82

78

 

 

 

 

 

 

Climb 2000'-3000' (sec)

60

60

60

 

60

RPM  @ 55 kts climb

5180

5100

5350

 

5100

 

 

 

 

 

 

Static Thrust (kg)

194

196

184

196

186

Static RPM

5020

5000

5400

4920

4880

 

 

 

 

 

 

 

 

 

 

 

 

Manifold Pressure

 

 

 

 

 

26" @ 2000' WOT

5800

 

 

5800

6000

25"

86 @ 5380

 

 

87 @ 5260

86 @ 5540

22.5"

77 @ 4780

 

 

76 @ 4680

76 @ 4940

 

 

 
Warp Drive
  
                     Warp Drive                                                    Warp Drive hub with drive lugs
  
  
The Warp Drive props are so widely distributed and known that I’ll use it as the standard for comparisons.  I’ll keep referring comparisons to the Warp because it’s the best-known prop of the lot. 
 
The Warp Drive is certainly the strongest of the lot – as others have said, “You could chop wood with them!”  I have a broken one from a wrecked 701 that we re-built, and can see that it’s solid carbon fibre and resin all the way through.  The lighter props will have foam cores.  Of course this makes the Warp Drive heavier and much greater rotational inertia.  It takes noticeably longer than lighter props to ‘spool up’ on opening the throttle, and stops with an almighty jolt on a 912S.  In my Rans S7 with the older flat-bed engine mounts this is alarming, but there have been lots of Warps on S7s for a long time so it doesn’t seem to cause any structural problem.  I believe the newer ‘focalized’ engine mounts on the S7 are much smoother, just as they are on the Savannah .  I have the straight blade Warp Drive, as it came on my Rans S7.  The tapered-blade model is reputed to have better efficiency and would have a lower rotational inertia, but I didn’t have one available for testing.
  

Those squared tips  are very strong and functional, but probably cause the greater noise that we noticed compared to the rounded, tapered ends of the other brands.  This strength and durability, and with the nickel leading edge makes the Warp a popular prop on float planes and dirt field use.
 
 The hub on the Warp Drive is particularly strong.  There are four clamping bolts on each blade mounting, and the butt of each blade is reinforced with an aluminum sleeve.  The hub uses the larger 101.6mm bolt pattern, with 13mm drive lugs that pass through the engine flange and into the prop hub – very strong, and maybe necessary with that high rotational inertia and those violent rotational jolts on start and stop....  Warp also insists on a squashplate on the front of the hub.
  
 On the Savannah , 12.5º at the tip gave 5800rpm at WOT.  At 600mm this measured to be 19.5º.
  
  
  
 Bolly
  
                                Bolly                                                                  Bolly hub
  
  

The Bolly props are an Australian design and well-known here as a high quality prop.  They tried having them made in China, but weren't satisfied with the quality, so are now manufacturing in Australia again.  They're now under new ownership with big plans to become a world prop manufacturer. 

 

Hans has been using a Bolly on his 701 for about 500hrs and loves it.  He went to the Bolly after his Woodcomp nicked the ground while taxiing through a dip and snapped off cleanly at the junction to the hub!  (The butt of the blade was seen to be hollow.....).
 
 The Bolly blades are considerably lighter than the Warp Drive blades, so the rotational inertia is noticeably less.  This makes it smoother running, and considerably less jolt on start and stop.  The blades are wider than the Warp and a more rounded shape as seen in the photos.  The 'Duratuf' leading edge protection is a heat-cured polyurethane, moulded into the leading edge.  It’s resilient and very effective protection against chipping.  The Bolly hub also uses the 101.6mm bolt pattern and drive lug system, particularly suitable for the 100hp engine.  It's very nicely machined, solid, and attractive so it doesn't really need a spinner.
 

The tips of the Bolly aren’t flat, so can’t measure pitch at the tip.  So I used the standard 600mm (2ft) out from the centre, where it measured 19º for 5800rpm WOT..

 

 

 
 
  
 Peszke

                                 Peszke                                                                Peszke hub
 
 
The Peszke props are made in Poland , and not widely distributed yet, but they are seeking distributors elsewhere.  I found the company very co-operative and easy to deal with.
 
As shown in the photos, the Peszke is certainly the most stylish and sharpest-looking prop of the lot.  The metallic silver/grey gel coat really sets it apart from the usual black ones.  The blades are slim and gracefully formed, with sexy up-turned tips to reduce vortex noise.
 
The hub is nicely machined and polished, and matching spinners are available.  The 75mm bolt pattern is used.
 
It’s a very light-weight prop, with the lowest rotational inertia of those tested, which makes it the smoothest running of the lot, and quite noticeably the quickest to speed up on opening the throttle, and less jolt on shut-down.  Despite the lesser blade area due to the slim blades, and 68” diameter, it cruised and climbed just as well as the much larger props.  Static thrust was 10 kg less than the Warp Drive (but 10 kg out of 190 is only about 5%), so take-off roll was a bit longer, but surprisingly, time-to-climb was very much the same, so the thrust must improve very quickly once the aircraft is moving.
 
There’s no separate leading edge protection.   The factory claims extra strength is built into the leading edge, but extensive dirt-field use might bring some chipping of the surface unless leading edge tape is used....   
 
I’ve lost the pitch settings that I used for the Peszke.....
All in all it’s a very nice prop, and performed really well.  I think it's ideally suited for the 80hp Rotax.  
This prop is now on a Zenith 701 with 80hp, and performing really well.
 
 

Brolga
                              Brolga
 
The Brolga is very different construction to the others.  It uses a composite hub made by Ultraprop in the USA , but the blades are made in Australia .  The original Ultraprop blades are flat, with no helix at all, but the Brolga blades have some helix – not as much as is optimum, due the limitations of the pitch blocks in the hub.  The pitch is adjusted by changing sets of tapered blocks that hold the blades in the hub.  These blades were designed for the 50-60 knot ultralights and trikes, and have been very popular on those machines. 

The relatively flat blades give good performance at those speeds, and excellent take-off performance, but I expected that they would run out of puff at higher speeds compared to the high-helix props like the Bollie and the Kool.  But testing shows this not to be the case, in that at the same manifold pressure settings, the Brolga performed at 86kts, within one knot of both the Warp and the Kool!  The pitch blocks only come in one degree steps.  16º is a bit too fine for cruise, giving WOT 6000rpm, but 17º is over-pitched for best take-off.  Since the Brolga is under-pitched, the rpm for the same manifold pressure setting is higher, but the speed was still the same......  I had expected that this large 4-blade prop would be best at take-off and noticeably slower at such speeds, but it seems not to be the case.......  At WOT it gave 100+ knots, same as all the others, which was really surprising!

I’ve used this Brolga for 400hrs, and the only down-side is that, on long trips alongside a Kiev on another Savannah , the Brolga consumes one litre/hr more fuel, probably due to the extra drag of the 4-blade configuration, but I can’t measure a difference in testing.  4-blades is necessary with the Brolga because the three-blade cavitates some on take-off.  Of course the 4-blades made for a smooth running and quiet prop, despite it’s rather ‘agricultural’ look. 

I originally chose the Brolga because the factory is nearby, the price was right, and I have had good performance from them on earlier ultralights for 1200+hrs. 

Unfortunately the Brolga is now out of production.......

 

 Kool

 
 
                              Kool                                          Kool hub                                      Kool tip
 
  
The Kool prop is made in Russia , and is beautifully designed.  It’s like a piece of sculpture, with flowing lines and not a flat spot anywhere.  Even the back surface is slightly concave.  The airfoil is thick and highly cambered, like a high-lift wing, and has a wide chord.  The core must be foam to have this light weight, but the thickness of the section, with the carbon fibre skin, makes a blade with great rigidity and stiffness.  The surface is a mirror-finish gloss black gel coat that looks great when new, but it does mark easily.....  The leading edge protection is stainless steel, moulded into the leading edge at manufacture, with ‘rivets’ embedded in the composite going right through from one side of the blade to the other.

It runs as smooth, and stops with much less jolt than the Warp.  Ground observers noted that the noise produced at cruise and full power at 800ft AGL was considerably less than the Warp.  Kool also produces a version with anti-vortex tips to reduce noise even further.  I know of a Savannah that has that prop, and we’ll do a noise comparison when we can get together.

The hub is fairly plain, with a matt black finish.  It uses the standard 75mm bolt pattern.

For 5800rpm WOT in the Savannah , the tip was set at 11.25º.  At 600mm from the centre the pitch measured 17.5º.